The valve train in a push rod engine uses a roller lifter which is installed in a lift guide. The roller lifter is acted on by a cam of the cam shaft which, in turn, acts on a push rod of a cylinder in the engine. The lift guide is used to prevent rotation along the axis of the roller lifter. In some applications, the lifter has to be installed in a unique position and in these cases, the lift guide often acts to orient the roller lifter.
Conventionally, the outer surface of the roller lifter interacts with the lift guide to prevent rotation and to provide proper orientation of the lift guide in the roller lifter.
Having the lift guide interact with the outer surface of the roller lifter has a number of disadvantages to include the sliding surface between the cylinder block and the lifter is reduced because a portion of the outside surface of the lifter is used for an anti-rotational feature; some of the mass of the lifter is accounted for by the anti-rotational guide; inertia forces are higher; the performance of the valve train is hampered by the increased weight and there is a cost associated with the increased mass employed in the roller lifter.